I have a pigeon egg and it is vibrating what does this mean? Is there a chick in there?

have a mamma pigeon that was given to me by rehabber. Unable to release due to eye injury. Well, two days after arrriving here she laid 2 eggs. AFter talking to many people I decided to let her keep them. Everyone said they are most likely not fertile. She has had them for about 11 days. Last night I went to clean her nest and picked one up to move it and it vibrated. I almost dropped it because it scared me. It was vibrating today some to. I tried to candle with a flashlight but did not see much. Does this mean it is fertile and there is a squab in there or is the egg getting ready to blow up like some other people have suggested which seems unlikley to me. Any information would be appreciated. I dont want to hurt the eggs by moving them. I am careful. Thanks Beth